Converting solar energy to electric power holds great promise as a renewable clean energy source. DSSCs have attracted tremendous attention in recent years because of their low cost and high efficiency. The DSSCs with the highest power conversion efficiency are based on liquid electrolytes, with a reported efficiency of over 12%. However, liquid electrolytes limit the long-term stability of DSSCs as leakage and solvent evaporation may occur. Efforts have been made to replace the liquid electrolytes with solid-state materials, including inorganic hole conductors/p-type semiconductors, organic hole conductors, nano-composite materials, and gel and polymer electrolytes. Among these materials, polymer electrolytes are of interest for practical applications owing to their excellent characteristics such as easy fabrication, low cost, good stability, and flexibility. However, after cells made from such materials degrade, power conversion efficiency values of the cells remain compromised.
Therefore, it is a primary object and feature of the present invention to provide a system and/or method for recovering performance of degraded solar cells.
It is a further object and feature of the present invention to provide a system and/or method for recovering performance of degraded dye-sensitized solar cells that can be performed on-site without removing the degraded dye-sensitized solar cells from a solar power system.
It is a still further object and feature of the present invention to provide a system that improves the performance of a degraded solar cell by applying at least one voltage pulse across the solar cell.
In accordance with the present invention, a method of recovering performance of a degraded solar cell is provided. The method includes connecting a power source to first and second electrodes of a solar cell. A first voltage pulse is applied with the power source across the solar cell so as to provide a forward electrical bias of the solar cell.
In accordance with another aspect of the invention, the forward electrical bias may include applying a second or more voltage pulse(s) spaced in time from the first voltage pulse. An electrolyte of the solar cell has ion transport channels defined therein. Electrons may be injected into the electrolyte for redistributing ions within the electrolyte so as to improve a flow characteristic through the ion transport channels.
In accordance with another aspect of the invention, the method includes converting solar energy to electrical energy in a solar cell having a first electrode and a second electrode arranged on opposing sides of an electrolyte. A solar cell polarity is defined between the electrodes during use corresponding to a voltage defined across the solar cell during use. A concentration of ions in the electrolyte is established corresponding to a degraded performance state of the solar cell having a first value of power conversion efficiency. In the degraded performance state, the solar cell is relatively less efficient and provides relatively lower photocurrent values than a solar cell with an undegraded performance state such as a newly manufactured solar cell. A power source is connected to the first and second electrodes and a voltage pulse(s) is applied with the power source across the solar cell. The voltage pulse(s) may be provided at the solar cell polarity, to provide a forward electrical bias of the solar cell so as to inject electrons into the electrolyte during application of the voltage pulse. The electrons may be injected through the photoelectrode, into the electrolyte. This may be done by injecting electrons from the conduction band of the photoelectrode to the redox level of the electrolyte. Ions may be redistributed in the electrolyte. This may be done by changing the concentration of ions in the electrolyte or attenuating some other blocking or flow restricting mechanism that is compromising performance of the degraded solar cell 14, which may open previously blocked ion transport channels. Opening the previously blocked ion transport channels may improve performance of the degraded solar cell, providing a recovered performance state having a second value of power conversion efficiency that is relatively higher than the first, degraded, value of power conversion efficiency. This may allow for recovering performance of degraded solar cells.
In accordance with another aspect of the invention, each voltage pulse may be between about 2 V and 3 V, such as about 2.5 V, and have a duration of between about 150 ms and 200 ms, such as about 185 ms, or other suitable voltage magnitudes and durations. This may provide pulse shapes that correspond to a rectangular wave form. The forward electrical bias may include applying multiple voltage pulses that are spaced from each other. The multiple voltage pulses may be provided as a double pulse delivery, a series of double pulses, or three or more pulses that have delivery times that are generally equally spaced from each other. Delivery of the pulses within the double pulses may be spaced from each other by a time period of between about 1 and 3 seconds, such as about 2 seconds, or other suitable time period. In this way, an integral value of a function that is represented in a voltage pulse graph showing the pulse(s) may correspond to an acceptable value of stimulus for recovering the degraded solar cell by forward electrical biasing. This may allow for injecting electrons in a manner that redistributes ions in the electrolyte in a highly controlled manner so as to avoid pulse-induced dark currents that are too large for maintaining the integrity of the solar cell.
In accordance with another aspect of the invention, an ion-related value may be determined that corresponds to a number of ions in the electrolyte. Based at least in part on the determined ion-related value, an electron-related value may be determined that corresponds to a number of electrons to be injected into the electrolyte during application of the voltage pulse. Based on such determined ion- and electron-related values, a number of electrons may be injected into the electrolyte with the voltage pulse(s) during the forward electrical biasing of the solar cell. The number of electrons may be no more than about the number of ions in the electrolyte. This may help maintain the integrity of the solar cell turning the forward electrical biasing of the solar cell.
In accordance with another aspect of the invention, a system for recovering performance of a degraded solar cell is provided that includes a solar cell defining a first electrode and a second electrode arranged on opposing sides of an electrolyte and defining a solar cell polarity therebetween during use. A power source is operably connected to the first and second electrodes. A controller is operably connected to the power source for controlling the power source to apply a voltage pulse across the solar cell at the solar cell polarity which may redistribute ions in electrolyte for improving the power conversion efficiency of the solar cell.
In accordance with another aspect of the invention, the solar cell may be a dye-sensitized solar cell with a non-liquid electrolyte. The electrolyte may be made from a solid-state material which may include a polymeric material. The electrolyte may be made from a quasi-solid-state material which may include a gel that may include a polymeric material. The polymeric material may be polyvinylidene fluoride.